This is the worst flu season nationally and in Massachusetts in several years, and the state's public health officials are urging people to take the outbreak seriously.

Clinicians and local boards of health have reported 18 flu-related deaths to the Massachusetts Department of Public Health this flu season. There are no reports of deaths among children, according to the state DPH, and most of the flu deaths involve elderly people with underlying medical conditions.

Six people have died from flu-related illnesses in Worcester area hospitals and nursing homes since the start of the flu season in late September, according to Derek S. Brindisi, the city’s director of public health. All of those who died were over 70 years old, he said.

At the end of December, the state had about 2,000 laboratory-confirmed flu cases.

In the city of Worcester, there have been 361 confirmed cases, of the flu, Mr. Brindisi said, with another 124 cases in five communities contiguous to Worcester that the city’s health department serves. But those are cases in which the cases were sent to the state laboratory for confirmation, he said. Many people will simply suffer through the symptoms and not be tested.

“It is certainly under-reported,” he said of the number of total cases of the flu, versus the number of confirmed cases.

Last flu season was mild, he said. This year, it is moderate to severe.

“The hospitals are being inundated with people presenting with flu-like symptoms,” he said.

At UMass Memorial Medical Center, officials have implemented a “flu season” visitation policy that asks that children under 14 years of age not visit patients at the center’s University and Memorial campuses. They have also asked that anyone with any flu symptoms — or have come in direct contact with someone who has the flu — not visit patients.

“This is a practice we have used many times in the past when cases of flu have surged in the region,” said Robert Brogna, UMass spokesman. “Except under extraordinary circumstances, visitors are being limited to immediate family, only two per patient, those who are 14 and older, to those without fever, cough or respiratory symptoms, and those visitors who have had no contact with someone with flu-like illness in the last 2 days.”

State and local health officials are encouraging people to get flu vaccines, since the flu typically peaks in February and can last well into the spring. There is an ample supply of flu vaccines across Massachusetts.

Everyone over the age of 6 months should get a flu shot, according to the state’s public health officials.

Mr. Brindisi said that children, the elderly, and people who have compromised immune systems are more susceptible to the flu, he said, and it is even more important for people in those categories to get a flu vaccine. In the 2009-2010 flu season, city health officials also learned that obese people tend to have more complications from the flu, and should get a flu vaccine.

Public health officials have also distributed nearly 840,000 free doses of the flu vaccine this flu season, primarily to community health centers and homeless shelters.

Shots are available at local pharmacies. Individuals without insurance can go to a community health center to get shots.

The good news, according to the DPH, is that the strains of flu virus in circulation this year were anticipated, and 91 percent of the viruses found in testing this year are well-matched to the vaccine.

The flu shot is the single most effective way to protect yourself and your family against the flu, the DPH said.

There are other ways to slow the spread of flu: Wash your hands often, and cover your cough or sneeze with your sleeve instead of your hands.